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UNIVERSITI TUN HUSSEIN ONN MALAYSIA
PENGESAHAN STATUS LAPORAN PROJEK SARJANA
PARTIAL DISCHARGE DETECTION FOR CONDITION MONITORING OF AN 11-KVXLPE CABLE
Saya NOR AKMAL BT MOHD JAMAIL mengaku membenarkan laporan projek sarjana ini disimpan di Pefpustakaail dengaa syafat-syafat kegunaan sepeiti befikut:
1. Tesis adalah hakmilik Universiti Tun Hussein Onn Malaysia. 2. Perpustakaan dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi
pengajian tinggi. 4. **Sila tandakan (V )
SESI PENGAJIAN: 2007/2008
SULIT (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972)
TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisaslTjadan di mana penyelidikan dijalankan)
V TIDAK TERHAD
(TANDATANGAN PENULIS)
Alamat Tetap:
KG SUNGAILIMAU, IJOK, 34510 BATU KURAU, PERAK.
PROF. MADYA DR. ZAINAL ALAM BIN HARQN (Nama Penyelia)
Tarikh: / »l / p 7 Tarikh:
CATATAN: ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak
berkuasa/organisasi berkenaan dengan menyatakan sekali tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
"I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in
terms of scope and quality for the award of the degree of
Master of Engineering (Electrical.)
Signature
Name of Supervisor
Date
PM.Dr.ZAMNAL ALAM B.HARON
* > £ N o v O o 0 ^
PARTIAL DISCHARGE DETECTION FOR CONDITION MONITORING OF
AN 11-KV XLPE CABLE
NOR AKMAL BT MOHD JAMAIL
A thesis submitted
In fulfillment of the requirement for the award of the Degree of
Master of Engineering (Electrical)
Faculty of Electrical and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
NOVEMBER, 2007
i i i
DEDICATION
This is special dedicated to
my beloved husband,
Qamarul Ezani B. Kamarudin,
my lovely newborn son,
Muhammad Ammar Syafiq,
and my family for their continuous love and prayers,
also to all my friends for their patient, kindness and cooperation .
I wish to thanks all of you for your support during my studies in UTHM.
May God bless all of them.
iv
ACKNOWLEDGEMENT
In the name of Allah S.W.T., the Most Beneficent, the Most Merciful.
Foremost, all praise to Allah for the entire incredible gift endowed upon mc and for
giving me the health and strength to complete this final project.
I am deeply grateful for the help that I received from my supervisor,
Associate Professor Dr. Zainal Alam bin Haron during this development of this
project. His willingness to help and ideas has kept me on my toes from the beginning
stage of this project until the completion of this thesis.
Many thank to P M Tarmidi Tamsir and Mr. Anuar, whom have given me the
convenience to approach all facilities available in the IVAT, UTM.
Special thanks to my lovely husband, Qamarul Ezani B. Kamarudin and my
son, Muhammad Ammar Syafiq for their support and encouragement. Also thanks to
Mrs Zuraidah Ngadiron for her help either directly or indirectly throughout the
preparation of this thesis and this project.
Last but not least, these special thanks go to my parents and family for their
faith and prayers that has enable me to succeed.
V
ABSTRACT
High voltage insulation failure has been a main cause of high voltage systems
for a long time now. It is found that this phenomenon occurs due to the existence of
partial discharge in voids found in insulation of cables, especially XLPE (Cross-
linked polyethylene) cables. Partial discharge normally exists in voids in cables
which are produced accidentally during the extrusion process of cables. However,
improvisation of XLPE cables from one generation to another generation has reduced
voids gradually and thus, reducing the threat of partial discharge. Yet, the effects of
partial discharge could not be underestimated as it would lead to serious breakdown
and electrical apparatus failure. Therefore, partial discharge testing by using a partial
discharge detector is one of the main tests used to determine the quality of the XLPE
cable so that the necessary steps and precautions can be made on the cable if the
cable does not meet the requirements of the test. In this project the insulation
condition of an XLPE cable with different types of artificial defects will be tested for
partial discharge and the results analysed and discussed. The complete procedures for
doing the testing are also described in this thesis.
vi
A B S T R A K
Kerosakan penebatan voltan tinggi telah menjadi punca utama tcrhadap
sistem voltan tinggi sejak kebelakangan ini. Didapati bahawa fenomcna ini berlaku
disebabkan oleh kewujudan discas separa di dalam ruang atau lubang yang didapati
pada penebatan kabel terutama kabel jenis XLPE (Cross-linkedpolyethylene).Discas
separa kebiasaannya wujud di dalam ruang atau lubang pada penebatan kabel yang
berlaku ketika proses penyemperitan kabel. Walau bagaimanapun, inovasi terhadap
kabel telah berlaku dari satu generasi kepada satu generasi untuk mengurangkan
ruang pada kabel dan seterusnya mengurangkan kejadian discas separa. Sehingga
kini, kesan terhadap discas separa tidak dapat dihapuskan dan ia akan menyebabkan
berlakunya pecah tebat yang serius dan seterusnya berlakunya kerosakan perkakasan
eletrik. Oleh sebab itu, pengujian discas separa dengan menggunakan pengesan
discas separa TE 571 adalah merupakan pengujian yang penting untuk menentukan
tahap kualiti kabel XLPE maka langkah yang sepatutnya diambil terhadap kabel
tersebut boleh dilakukan jika kabel tersebut tidak memenuhi kriteria yang ditetapkan.
Projek ini akan membincangkan tentang keadaan penebat kabel XLPE yang
mempunyai kerosakan buatan yang berbeza berdasarkan kepada pengujian discas
separa dan prosedur yang lengkap untuk melakukan pengujian discas separa
dibincangkan dalam tesis ini.
V I I
TABLE OF CONTENTS
CHAPTER ITEM
SUPERVISOR DECLARATION
TITLE
DECLARATION
DEDICATION
ACKNOWLEDGEMENTS
ABSTRACT
ABSTRAK
CONTENTS
LIST OF TABLE
LIST OF FIGURE
SYMBOLS/TERMS
LIST OF APPENDIX
I INTRODUCTION
1.0 Introduction 1
1.1 Partial Discharge Phenomenon: Terminology 3
1.2 Background of the Problem 4
1.3 Objectives 4
1.4 Project Scopes 5
1.5 Significant Of the Project 5
1.6 Thesis Layout 6
PAGE
l
ii
v
v
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x i i
x i i i
x v i
x v i i
LITERATURE REVIEW
2.0 Partial Discharge Detection
2.1 Gas /Vacuum as Insulator
2.2 Liquid Dielectric
2.3 Solid Dielectric
2.4 Applications of Insulating Materials in Cables
2.4.1 Polymeric Insulation
2.5 Introduction of XLPE Cables
2.5.1 Failure of the Cable
2.6 Partial Discharges
2.6.1 Classification
2.7 Inception of Internal Discharges
2.7.1 Gas-filled Cavities
2.7.2 Inclusions
2.7.3 Oil-filled Cavities
2.8 Inception of Surface Discharges
2.9 Inception of Corona Discharges
2.10 Discharges by Electrical Treeing
2.11 Partial Discharge in Cable
2.12 Insulation System Model
2.13 Parti al Discharge Void Model
2.14 Quantities Related to the Magnitude of Dischargi
2.14.1 Charge transfer
2.14.2 Apparent Charge Transfer in the Sample
2.14.3 Discharge Energy
2.14.4 Dielectric Losses Due to Discharges
2.14.5 Integrated Quantities
2.15 Breakdown Due to Internal Discharges
2.16 Detection Methods
2.16.1 Electrical Detection
2.16.2 Optical Detection
ix
2.16.3 Chemical Detection 26
2.16.4 Acoustic Detection 27
2.17 Partial Discharge Measurement 28
2.17.1 Introduction 28
2.17.2 Discharge Detection Using Straight Detectors 28
2.17.3 Discharge Measurement for Cable 31
2.17.4 Calibration of Discharge Detectors 33
2.17.5 Discharge detection in Power Cable 33
DESCRIPTION OF THE EQUIPMENT AND MATERIALS
3.0 Introduction 36
3.1 System Components 36
3.1.1 TE 571 Detector 36
3.1.2 AKV Coupling Quadripole 37
3.1.3 Special Cable 38
3.1.4 AC Test System Operating Terminal 39
3.1.5 PD Calibrator (KAL 450) 39
3.1.6 Apparatus and Their Function 40
3.2 Mains and Earth Connections 42
3.2.1 Main Connection 42
3.2.2 Earth Connection 43
3.2.3 Computer Connection 43
3.2.4 Instrument Front Panel PD Detector 43
3.2.4.1 Monitor 43
3.2.4.2 Data Memory 44
3.2.4.3 Keyboard 44
3.2.4.4 Mouse Connection 44
3.2.4.5 Front Panel Controls 44
3.3 Connecting the AKV 45
3.3.1 Connections for Standard Use 45
3.3.2 Connection for Use with Additional Secondary Unit 46
3.3.3 Current Range Selection 46
3.4 Operation 46
3.4.1 TE571-OSW Office software introduction 47
3.4.2 PD-Scope™ 48
3.4.3 Functions of Key Fl-F 10 49
3.4.3.1 Help 49
3.4.3.2 Config 49
3.4.3.3 Calibration 50
3.4.3.4 Main Menu 50
3.3.4.5 Pause 53
3.3.4.6 F6~PD Units 53
3.3.4.7 Windows 54
3.3.4.8 Auto Record 54
3.3.4.9 Manual Record 55
3.3.4.10 Print 55
3.4 Test Circuit Construction 56
METHODOLOGY
4.0 Introduction 57
4.1 Preparation Prior to Perform the Testing 5 8
4.1.1 Safety Precautions 59
4.2 Launching the Display of TE 571 Detector 60
4.3 Partial Discharge Level Calibration 61
4.4 Voltage Calibration 63
4.5 Test Procedures 65
4.6 Testing Circuit Arrangement 68
xi
Insulation
5.1.2.7 PD Level Corresponding to Injected 86
Voltage
5.3 Summary 89
VI CONCLUSIONS AND RECOMMENDATIONS
6.0 Conclusions 90
6.1 Recommendations 91
REFERENCES 92
APPENDICES 95
69
70
70
74
75
77
79
81
V RESULTS & DISCUSSION
5.0 Introduction
5.1 Testing Results
5.1.1 Calibration results
5.1.2 Cable Testing and Measurement Results
5.1.2.1 Case A: Cable in Good Condition of
Insulation
5.1.2.2 Case B: Void between Cable Insulation
and Iron
5.1.2.3 Case C: Void between Cable Insulation
and Aluminium
5.1.2.4 Case D: Void between Cable Insulation
and Copper
5.1.2.5 Case E: Olive Oil Effect on the Test Cable 83
Insulation
5.1.2.6 Case F: Grease Oil Effect on the Test Cable 84
xii
LIST OF TABLE
NO. OF TABLE TITLE
2.1 Cable insulation 11
2.2 Insulation and technology of H V cables 12
3.1 Electrical apparatus and their function 40
xiii
LIST OF FIGURE
NO. OF FIGURE TITLE PA
2.1 Corona at sharp edges (opposite electrodes at a 17
fair distance)
2.2 Simplified insulation model and model for an electronic 19
attenuator
2.3 Simplified partial discharge void model with internal 20
resistive leg
2.4 Electrical discharge in a cavity and its equivalent circuit 24
2.5 Sequence of cavity breakdown under alternating voltages 24
2.6 Straight discharge detection circuit 29
2.7 Partial Discharge patterns 31
2.8 Equivalent circuit of the cable for discharges 32
2.9 Discharge detector connection to long length of cable 32
2.10 Partial discharge testing arrangement for distributed 35
parameter equipment (cables, transformer windings, etc)
3.1 Partial Discharge Detector 37
3.2 AKV Coupling Quadripole 38
3.3 System component-AKV 573 Coupling Quadripole 38
3.4 AC test system operating terminal 39
3.5 Partial discharge calibrator (KAL 450) 40
3.6 High voltage transformer 41
3.7 Resonant high voltage transformer and HAEFELY 41
coupling capacitor
3.8 AKV 573 connections 45
3.9 PD Scope with ellipse 48
3.10 Main menu display 50 3.11 Typical PD Test Circuit Arrangement 56 4.1 The Flow Chart of the project 58 4.2 The display of configuration for F2 key 60 4.3 Block diagram of PD level calibration 61 4.4 PD calibration menu 62 4.5 PD Scope display after PD level calibration success 63 4.6 Block diagram of voltage calibration 63 4.7 PD Scope display after PD level and voltage calibration 65
success
4.8 Display of test identification 66
4.9 Auto Record display that displays the information about 67 the user
4.10 The partial discharge test circuit arrangement 68
5.1 Partial Discharge Detector 69
5.2 The Arrangement of 1 lkV XLPE Cable 70
5.3 PD Scope display before calibration is done 71
5.4 Display of PD level and voltage calibration 72
5.5 Display of PD level calibration was success 72
5.6 Display of sinusoidal wave when the high voltage is 73
injected to the Partial Discharge Detector TE 571
5.7 Display of PD level and voltage calibration were success 73
5.8 PD Scope display for cable in good condition of insulation 76
5.9 Line diagram for testing the cable in good condition of 77
insulation
5.10 PD Scope display for void between cable insulation and 78
iron
5.11 Line diagram for void between cable insulation and iron 79
5.12 PD Scope display for void between cable insulation and 80
aluminium
5.13 Line diagram for void between cable insulation and 80
aluminium
5.14 PD Scope display for void between cable insulation and 81
copper
5.15 Line diagram for void between cable insulation and 82
copper
5.16 PD Scope display for olive oil effect on the test cable 83
insulation
5.17 Line diagram for olive oil effect on the test cable insulation 84
5.18 PD Scope display for grease oil effect on the test cable 85
insulation
5.19 Line diagram for grease oil effect on the test cable 85
insulation
5.20 PD values and cable performance of XLPE cable 88
according to different voltages
5.21 PD values and cable performance of XLPE cable 89
according to different voltages
LIST OF ACRONYMS/SYMBOLS/TERMS
Partial Discharge
High Voltage
Cross-linked polyethelyne cable
Kilo Volt
Sulphur Hexafluoride
International Electrotechnical Commission
Universiti Teknologi Malaysia
Polyvinyl Chloride
Polyethylene
Ethylene-propylene
Pico Coulomb
Nano Coulomb
MegaHertz
Dissolved gas analysis
High performance liquid chromatography
Kilo
Cable transit time
relative permittivity of the dielectric
Coupling quadripole
Mega
Frequency
xvii
LIST OF APPENDICES
APPENDIX ITEM PAGE
A FIGURES OF THE SETTING EQUIPMENT 95
B TABLE OF THE RESULTS 97
CHAPTER I
INTRODUCTION
1.0 Introduction
Partial discharge detection is nowadays a very well established method for
monitoring the insulation condition of an electrical apparatus. The breakdown of
insulation while in service can cause considerable damage to an apparatus and to the
system to which it is connected. It has been recognized that failures of this type often
may be related to the occurrence and severity of partial discharges within voids
and/or on the surface of the insulation. Testing of high voltage apparatus for partial
discharges has long been recognized as an important part of quality control for these
devices [1].
Partial discharge, as implied by its name, is a type of localized discharge
resulting from transient gaseous ionization in an insulation system when the voltage
stress exceeds a critical value. The ionization is localized over only a portion of the
distance between the electrodes of the system. The resultant partial discharge signals
appear as very small magnitude, fast rise pulse (10-100ns) with irregular waveshapes.
Partial discharges do not cause complete breakdown of the dielectric [2].
In practice, four types of partial discharge may be identified; they are,
namely, Internal Discharge, Surface Discharge, Corona Discharge and discharge in
electrical trees [13]. In insulation systems with strongly inhomogeneous field
2
configurations or inhomogeneous dielectrics, the breakdown field strength can be
locally exceeded without complete breakdown occurring within a short time. Under
this condition of incomplete breakdown the insulation between the electrodes is only
partially bridged by discharges. These partial discharges have considerable practical
significance particularly for the case of stress by alternating voltages. Partial
discharges cause deterioration of insulation materials and are a primary cause of
insulation failure at moderate and high voltages especially due to surface or internal
discharges or treeing. The electric strength of solid insulation may decrease greatly
with time of voltage application if discharge occurs within gaseous inclusions, at
sharp-edged conductors embedded in the solid and as a result of surface
contamination.
Partial discharge measurement is a very well known method for assessing the
quality of an insulation system of high voltage devices, because the life of high
voltage equipment depends on the presence of partial discharge. The aim is to detect
the initial destruction in the electrical insulation as a result of electrical stress. The
presence of a multiplicity of different partial discharge sources and their appearance
shows different physical and electrical characteristics. For the economic use of high
voltage operational equipment, it is necessary to always know the condition of the
equipment in service. That is the reasons why monitoring, analysis or diagnosis
become a fixed part in power generating, transmission and distribution systems. In
this area the partial discharge measurement is an important diagnostic tool.
A Partial Discharge (PD) measurement is used as one of the quality control
test for extruded cables in the medium and high voltage range. The normal situation
would be that partial discharges would not occur in such cables when energized to
stresses usually required in specification. Occasionally, however, there will be an
isolated defect which does produce PD [14].
Cables constitute one very important electrical apparatus for transmission of
electrical energy by underground means. Large power transmission cables are of
importance and hence testing of power cables is considered a must. Partial discharge
measurement and the discharge locations are important for cables, since the life of
3
the insulation at a given voltage stress depends on the internal discharge. Also the
weakness of the insulation or faults can be detected with the help of this test.
For maintenance purposes, early detection of discharges in cables is an
important diagnostic tool to assess the cable condition and if possible to locate the
defect, especially since it highly undesirable to have to remove the cables from the
operation even for occasional Partial Discharge testing.
A point of significant practical implication is the fact that surge propagation
in the cable is affected by attenuation as well as wave shape deformation. This fact is
fully exploited in the partial detection method as the principal means for detecting
and locating partial discharge occurrences in cables. Progress in cable insulation
design, such as the inclusion of semiconducting layers to give a uniform electric field
distribution, and hence result in less partial discharge occurrences and a better over
voltage control, on the downside causes more significant PD signal deformation
during propagation. Since an XLPE cable's insulation is very sensitive to partial
discharges occurring within itself, fast PD detection by online monitoring is essential,
and therefore a detectable signal is needed to be picked up at the monitoring
terminals.
1.1 Partial Discharge Phenomenon: Terminology
Partial discharge is an electrical discharge that only partially bridges the
dielectric or insulating medium between conductors. Examples are: internal
discharges, surface discharges and corona discharges. Internal discharges are
discharges in cavities or voids which lie inside the volume of the dielectric or at the
edges of conducting inclusions in a solid or liquid insulating medium. Surface
discharges are discharges from the conductor into a gas or a liquid medium and form
on the surface of the solid insulation not covered by the conductor. Corona is a
discharge in a gas or liquid insulation around the conductors that are away or
removed from the solid insulation [11].
1.2 Background of the Problem
4
Testing of high voltage apparatus for partial discharge is an important part of
quality control. Weak points in an insulation like voids, cracks and other
imperfections lead to internal or intermittent discharges in the insulation. These
imperfections being small are not revealed in capacitance measurements but are
revealed as a power loss component. Partial discharge in voids may cause
deterioration of solid insulation materials. They often start in voids enclosed in the
insulation or at the interface defect. Partial discharge is a major source of insulation
failure in a cable. The accurate location of the discharge is of crucial importance in
on-site maintenance and repair. This project will concentrate on partial discharge
detection to determine the insulation condition of the cable.
1.3 Objectives
The objectives of this project are:
i. To prepare the complete test procedures for partial discharge detection of
XLPE cables by using the PD detector, TE 571.
ii. To test the condition of cable by the method of partial discharge detection.
iii. To detect the partial discharge of cable for assessing the likelihood of a
fault on a cable containing an incipient defect.
iv. To study the partial discharge patterns and to interpret the condition of the
cable with different types of artificial defects.
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